Wind parks usually comprise a plurality of wind turbines which are coupled via a main transformer to a power grid. Voltage imbalances may occur on the power grid. These voltage imbalances may be coupled into the wind park via the main transformer.
An unbalanced supply voltage from the power grid will typically give rise to a dc (direct current) link voltage variation at twice the line frequency in a grid-connected converter of the wind turbine. This dc voltage variation may result in an asymmetrical current with high total harmonics distortion (THD) if no voltage imbalance correction is implemented. Grid code requirements may not be fulfilled if an asymmetrical current with high THD is injected to the grid. Therefore, the grid code requirements may not be fulfilled due to the presence of voltage imbalances.
Further, the wind turbines may operate in an optimum efficiency in the presence of a balanced voltage. When the voltage is unbalanced, the efficiency of the wind turbines may reduce, which may result in a loss of power production of the wind turbines.
Hence, one objective of the present invention is to avoid the above-mentioned problems.